We propose to use a combination of two powerful techniques: aptamer selection (systematic evolution of ligands by exponential enrichment; SELEX) and in vitro compartmentalization (IVC), to develop a new method of generating libraries of functionalized nanoparticles and that can be screened directly for function. While the goal of this application is to develop a novel system for the direct identification of targeted nanoparticles which localize to human tumors, we will develop a platform technology which extends beyond the detection and treatment of cancer and other diseases and will result in the generation of a novel class of capture agents that will find use in a variety of applications and fields of research.